Aluminum vs. Titanium

In the chatroom entry, a consumer is asking for advice on aftermarket
tires for his new ultralightweight wheelchair. While tire
brands are his main question, he pauses to take a swipe at his new
ride. He mentions the brand and model of the chair, which is aluminum.

“That’s the best I can get out of Medicaid,” he typed. “I wanted
titanium.”

If you’re a complex rehab provider or clinician who works with
ultralight chair users, you’ve probably heard that comment over and
over. You may even hear it from industry professionals: “We want titanium!”
But when aluminum and titanium go toe to toe as today’s
materials of choice to create ultralight chairs, is one material clearly,
truly, always better than the other?

Introducing Our Contenders

Titanium’s discovery in the late 1700s is commonly credited to German
chemist Martin Heinrich Klaproth, who named the metal after the
Greek Titans, a clan of powerful gods and goddesses (including Zeus’
mom and dad, Rhea and Cronus). Among ultralight users today, titanium
continues to get the royal treatment. In other observed chatroom
conversations, ultralight chair users described titanium as “sexy” and
– in one humorous case – a “manly man” metal. Adding to titanium’s
seemingly elite status is its higher cost and its relative rarity, at least
compared to aluminum.

Aluminum, in contrast, is earth’s most abundant metallic element,
according to the Mineral Information Institute. While titanium’s name
was inspired by deities, aluminum’s origin is simpler. It comes from the
Latin word alum, a kind of mineral, in combination with the “-ium”
suffix commonly given to elements named in that same time period
(the 1820s). It’s “aluminum” in the United States, but “aluminium” in
Britain and other parts of the world.

Once upon a time, aluminum was called the “space-age” metal –
back in the days when steel was the other material choice for wheelchairs.
But that anecdotal honor has since been taken over by titanium.

So is titanium merely getting the credit it deserves, or is aluminum
perhaps underappreciated and misunderstood as a medium for ultralightweight
chairs?

We took our collection of assumptions – widely held and/or anecdotal
beliefs about titanium and aluminum – to a group of industry experts and
asked their opinions. Participating in our “search for truth” are…

Jim Black, Invacare Corp./Top End

Mike McCarthy & Mike Zablocky, Pride Mobility Products

Tom Whelan, Sunrise Medical

Josh Anderson, TiLite

Currently, Invacare, Sunrise and TiLite all offer both aluminum and
titanium ultralight chairs. Pride does not currently have a titanium
ultralight in its lineup, though Mike McCarthy says, “Titanium is definitely
something that is talked about internally, in addition to some
other hybrid materials.”

Assumption #1

Titanium Is Lighter

Perhaps the most common rationale for choosing a titanium chair over
an aluminum one is weight: Titanium chairs have historically been (or
have been presumed to be) lighter in weight than aluminum chairs,
and for the consumer who self-propels many miles in a lifetime, having
to push a chair that’s heavier than necessary can become a significant
physical burden.

So our first question: Is titanium lighter than aluminum?

Answer: No… and maybe.

“The perception out there is that titanium is lighter,” says Jim
Black. “Titanium is not lighter than aluminum.” As a raw material, titanium
actually weighs more than aluminum, though both metals weigh
considerably less than steel.

“Aluminum has one-third the density of steel,” says Mike Zablocky.
“Titanium is half the weight of steel, so because it has a lower mass, it
can be just as strong (as steel) at half the weight.”

Then why are titanium wheelchairs so routinely assumed to weigh
less than aluminum chairs if titanium weighs more than aluminum?
Chalk that up to the metals’ different properties and how they’re used
in the ultralight wheelchair manufacturing process.

Imagine that a wheelchair manufacturer is creating two identical
ultralight frames – one aluminum, one titanium – and wants to make
each frame as strong as a steel counterpart would be.

“You need more aluminum to equal the same amount of (strength
as) titanium,” Zablocky explains, noting that with titanium, “you can use thinner wall tubing to yield the same amount of strength.”

So aluminum as a raw material weighs less than titanium, but
because larger amounts of aluminum have needed to be used, titanium
chairs have historically been lighter in weight than aluminum
counterparts.

“You just have to use more aluminum to get to your outcome,”
Mike McCarthy says, “whereas with titanium, because of the strength
capabilities, you can use a thinner wall material. I think that’s where
the perception issue arises.”

But as manufacturing processes and wheelchair designs have
evolved, Tom Whelan says, it’s no longer a given that a titanium chair
will be inherently lighter than an aluminum one.

“In the past, all the lightest-weight chairs were titanium,” Whelan
acknowledges. But he references the bicycle industry: “The parallels
are just compelling, because 90 percent of what you see in wheelchair
technology as far as base material and material management flows from the bike industry. As aluminum bike frames have gotten lighter
and stronger, they’ve caught up with titanium.”

And now, Whelan says, evolving manufacturing techniques are
making it possible to work with aluminum in ways that weren’t
possible before. “There’s a technique called hydroforming, where you
can make an aluminum tube where it is thinner and thicker in the walls
along the length of the tube. I might need a slightly thicker wall where
I have to join two tubes with welding, but in the length of the tube, I
might not need that wall thickness.”

This ability to vary wall thickness can allow manufacturers to use
more aluminum only where they need to, and reduce the amounts of
aluminum they use in other areas. “Titanium can’t be hydroformed,”
Whelan says, “so (it requires) a uniform wall thickness throughout.
That’s a technique that’s helped aluminum catch up….You just can’t
make that claim anymore that titanium is lighter, therefore it’s going to
be a better chair.”

Aluminum vs. Titanium: The Funding Question

If there is any “sure thing” in the question
of titanium vs. aluminum for
creating ultralightweight chairs, it’s this:
Titanium costs more. Much more.

As a demonstration, Pride Mobility
Products’ Mike Zablocky says, “We just
took a very basic piece of quarter-inch
round rod, one foot long, and compared
the cost of (6061 T6) aluminum versus
grade 5 titanium. The aluminum was 32
cents for the rod, and the titanium was
$11.04 for that same rod. So there is a cost
difference.”

In addition to costing more from the
outset, titanium, our experts noted,
is more difficult to work with than
aluminum, which makes the manufacturing
process more expensive. “The
bending and grinding and welding of that
thinner tube and that wall thickness is a
very delicate process that requires some
skill,” Zablocky adds. “That’s not the case
with aluminum – it’s very easy to weld.”

As a result, there’s a common perception
that payors don’t buy titanium ultralightweight
chairs as readily as their less expensive
aluminum counterparts. It’s probably
more accurate to say that in many cases,
funding sources are willing to pay for titanium
chairs, but that those allowables don’t
always cover the chairs’ full costs.

Sunrise Medical’s Tom Whelan points
out that currently, CMS uses only a couple
of criteria to determine a manual chair’s
HCPCS code, which in turn determines
the chair’s allowable.

“Today, coding uses weight,” he
says. “It’s really the only characteristic
of propulsion in coding – weight and
certain characteristics of adjustment. So
if I have an adjustable axle and I have
lighter weight, I can get more money
for the chair. Which doesn’t necessarily
mean that every chair that’s lighter weight
and has adjustable axles will actually be
easier to propel, but yet that’s the basis of
separating those (chairs) from a coding
perspective.”

Whelan hopes projects such as the
Anatomical Model Propulsion System
(AMPS) currently underway at the
Georgia Institute of Technology (see main
story) could change that.

“AMPS could be a great way of saying,
‘(We) can develop a coding system around
actual propulsion efficiency, which means
I’ll be able to tell you which chair will actually
have the potential to reduce stress and
strain on the shoulders,’” Whelan notes.

Asked how ultralight funding is going
in state Medicaid programs, Invacare
Corp.’s Jim Black says, “It really depends
on the region. For example, Texas is really
one of the bigger states that provides a
lot of titanium products. Their Medicaid
system follows the Medicare guidelines,
but they utilize that K0009 (other manual
wheelchair/base) code, and K0005 as well.
In some states, they won’t even venture
into (using) a K0009 (code). So it really
depends on the state.”

TiLite’s Josh Anderson says funding for
titanium chairs can be hurt because “It
just so happens that aluminum is seen as
the ‘standard’ material for an ultralightweight
wheelchair. This wasn’t the case
30 years ago; back then, it was steel. But
now we know that aluminum offers better
properties for a wheelchair than steel. We
just need those individuals who make
funding decisions to take the next step
forward and recognize that titanium is a
better material than aluminum.”

Says Whelan, “CMS has been very clear
on this: If you want a new code or you
want to push reimbursement, you need
to bring to us valid research. What we
really want is randomized clinical trials,
which you rarely see in our industry. I
think we can push back on the problems
with statistically valid randomized clinical
trials, but only if we have really good,
pointed science that is pretty much unarguable.
So these projects like AMPS are
very important things.”

Assumption #2

Weight Is Everything

This one is closely related to the first assumption that titanium makes
for a lighter chair. Assumption #2 is that weight is extraordinarily
important to the ultralight chair user, to the degree that even shaving
a pound or two from the chair’s weight will make all the difference in
the world.

So is it true that weight is all important? Our experts largely agreed:
Yes for one particular situation, but for most other applications – no.

Let’s start with the situation for which the answer is yes.

Unlike most other wheelchairs, ultralights are routinely transported
in the passenger and back seats of cars, often by users who
transfer from their ultralights into their cars, then haul their chairs
in after them. For transportability – when users
or caregivers are hefting chairs into vehicles – the
weight of the chair is key.

“The only argument about (weight) that makes
sense and that you’ll hear from therapists is the
lifting weight,” Black says. “If someone is pulling it
in and out of the car, that’s important.”

Beyond transportability, however, our experts
didn’t buy the simple “weight is everything” argument.
Instead, they focused more on judging a
chair’s overall performance, including the quality of
its ride and how efficient it is to propel.

Aluminum and titanium both have inherent
characteristics that have made the metals favorite
choices among engineers.

“What makes aluminum a good material for
building a wheelchair frame is that it is very lightweight
and strong,” Josh Anderson says. “It is also
very stiff, which is good because it maximizes your
energy transfer – energy transfer is the movement of
energy from one place to another, in this case, from
your body to the wheelchair. Doing this as efficiently
as possible means that more of the energy you
expend goes into moving you forward.”

Anderson calls titanium “the ideal metal for
ultralightweight manual chairs,” noting, “The titanium
alloys used for wheelchairs were developed
for the aerospace industry and have some of the
highest strength-to-weight ratios of any metals.”
He also lauds titanium’s vibration-dampening abilities:
“Most metals transmit vibrations, but titanium
absorbs vibrations. This means that a titanium chair
will provide the smoothest ride. There are at least
two benefits to the smooth ride. First, a smoother
ride is more comfortable for the user. Second, the
less the chair bounces around, the more efficient the
propulsion. And the more efficient the propulsion,
the less fatigued the user will be.

“In part, this vibration-dampening effect is due
to the fact that titanium is not as stiff as some other
metals, such as aluminum, which is often why you see larger-diameter tubes on titanium cantilever frames. That largerdiameter
tube has more surface area and gives a titanium frame that
needed stiffness to maximize energy transfer.”

Overall, the experts found characteristics to praise in each metal,
even while differing as to whether titanium or aluminum gets the edge
in ride quality.

Black, who has worked internationally with elite wheelchair
athletes, says, “If you look at the sports products of the world, there’s
not a titanium sports product that any world-class athlete uses. It’s all
aluminum. And the reason for that is aluminum you can make lighter,
and aluminum you can make stiffer, so it has a more responsive,
energy-efficient ride.”

As an industry, Black adds, “We’re so concerned about weight.
Weight is relevant, but it really has nothing to do with how the chair
performs. So when you’re in the chair, especially these new openframed
designs, these monotube frames that everybody has now, they
flex so much that you lose energy. And when you put it in titanium,
they even flex more, so you’re losing energy. That means you have to
spend more time on your handrim, and you’re pushing longer. So the
reality is you’re losing your rollability of the product.”

Assumption #3

Aluminum Rides Better

Does that mean that aluminum actually holds an ultralight performance
advantage over titanium?

While Black says world-class wheelchair athletes don’t choose
titanium chairs for competition, he also adds, “The design has more
to do with it than anything. So a box frame or a frame that has
some triangulation or welds that come together as opposed to being
open is a better choice when you choose titanium, because titanium
moves so much.

“One of the things that other industries do, say the medical
industry when they replace joints – they use titanium because titanium
has a lot of the same properties as bone, for example. So it
moves and twists, and your bones are moving and twisting. But in a
wheelchair, you want something that’s going to be stiff and hold the
energy and make it more responsive. That’s why aluminum’s probably
the better choice, and it’s less expensive. I’d rather put more
money into the components of the chair than put it into the material
of the chair.”

Speaking of components, when it comes to ride quality, Black
suggests taking a closer look not necessarily at the metal making up
the frame, but at caster and wheel choices, such as “a rear wheel
that’s stronger and has less flex so you’re more efficient.”

As for titanium’s advantage in the vibration dampening department,
Black says, “If I was being pulled behind a car every day
at 30 to 40 mph, it would make a difference. But that’s not the
case. Justification (for an ultralight) should be designed around the
options you choose on a chair.”

On the subject of whole-body vibration, Whelan says, “If you’re
traveling over a rough road surface, you’re transmitting shock in
the form of vibration into the chair from going over pavement that
has gravel embedded in the pavement. Now the chair is seeing this
vibratory shock. It’s an oscillation that’s going on, and that vibration
is being absorbed by the body. There’s very clear evidence that
supports that wheelchair users will suffer from whole-body vibration.
The primary negative effect of absorbing that shock is fatigue.

“The issue of whole-body vibration is an interesting issue to
study. For the titanium material to have a positive effect, it has to
have a relationship to the frequency and magnitude of the shock.
If the vibration was a certain frequency, the material might actually
amplify the vibration. If it has a certain relationship, it might attenuate
the vibration.”

Whelan says an ongoing challenge for the assistive technology
field is to be able to scientifically measure outcomes such as wheelchair
ride and performance.

“If you had two chairs that were exactly identical in design and
the only variable was the material, then the material might make a
difference,” he says. “Then your question becomes how substantial
is the difference that it makes.… We have to deal with ‘What is the
measure that predicts performance?’ and ‘What are the performance
characteristics that are important to it?’”

Whelan adds that a range of factors – including a chair’s weight,
setup, wheel and tire selection, and rigidity – all contribute to how
well a chair rides and how efficiently it can be propelled.

“What has never existed in our industry and today still doesn’t
exist is an actual way of comparatively measuring a chair’s propulsion
efficiency,” he says. “There’s technology like the SmartWheel,
where I can put a wheel on a chair, and I can put a user in a chair,
and I can start theorizing that if I make changes to the chair or
compare two identically set-up chairs with identical wheels and
tires, that using the output of the SmartWheel, I might be able to
start comparing that.” But Whelan adds that conducting such a test
would assume “the person is able to put the same, identical energy
into the systems for that comparison. I haven’t met the perfect
human yet who can sit and push two chairs with the identical same
force two times to create that measurement.”

Whelan is enthusiastic about an ongoing Mobility Rehabilitation
Engineering & Research Center (RERC) project at the Georgia Institute
of Technology that could help provide answers. “The RERC which is
at Georgia Tech has instigated a project called AMPS (Anatomical
Model Propulsion System),” he says. “They’re going to build a functional
robot that can sit freely in a wheelchair and propel it.”

That robot could enable a researcher to “remove all the variables and
literally compare two chairs as far as their efficiency,” Whelan says.

Assumption #4

Titanium Is Stronger…

This is one of the few more straightforward questions about the two
metals.

“Titanium does have a better strength-to-weight ratio than
aluminum,” Whelan says. In a practical sense, that can equate to better
durability and easier upkeep for consumers.

“Titanium does not corrode or rust,” Anderson points out.
“Therefore, titanium does not need to be painted like aluminum to
protect it from the elements. If you scratch it, you can simply buff the
scratch out with a Scotch-Brite pad, like the kind you use to clean your
dishes. That makes keeping a titanium chair looking like new much
easier than any chair that needs to be painted.”

From an overall usage standpoint, Anderson also notes that titanium
“unlike aluminum, does not work-fatigue. Work-fatigue means
that over time, the material becomes brittle. For this reason, eventually
all aluminum frames will become prone to breaking. This is why
aluminum parts on airplanes must be replaced at specified intervals.
Because titanium is so strong and does not work-fatigue, durability is
greatly improved.”

Whelan agrees titanium has greater fatigue strength, but questions
the practicality of it: “If your goal in design was to build a wheelchair
that would be very, very light and last forever, you would lean towards
titanium, because the fatigue strength of titanium can be greater than
the fatigue strength of aluminum. However, let’s face it: No wheelchair
user wants a chair that lasts forever, because they want to benefit from
changes in design and changes that go on in the industry.

“There are very few wheelchair frames out there more than 10
years old. So you are always in design identifying a life cycle that you
design to. And exceeding that life cycle may not have any real value.”

Assumption #5

…But Aluminum Is Easier to Work With

For all its strength, titanium requires careful handling in a carefully
controlled work environment.

“When you’re working with titanium, it is far more challenging than
aluminum,” Zablocky says. “The bending and grinding and welding of
that thinner tube and that wall thickness is a very delicate process that
requires some skill. That’s not the case with aluminum – it’s very easy
to weld.”

Environmentally, titanium “is very susceptible to contaminants
during the manufacturing process,” Zablocky adds, “and you can end
up with a term they call embrittlement. So if you don’t take care, you
can end up with a stress point that will fracture because of poor manufacturing.
It’s a very thin wall, and it’s a very delicate process. It’s definitely
more difficult to fabricate.”

But cosmetically, Zablocky says, titanium gets the edge. “If you
weld it properly and you handle it and it does come out right, you get
a much smaller weld,” he explains. “It’s very clean, while typically with
aluminum, because the wall thickness is bigger, you get a slightly larger
weld bead.”

The message here may be that providers and clinicians who recommend
and sell titanium chairs should work with manufacturers who are
experts in handling the metal.

Says Anderson, “I don’t think any other frame material can match
its ride quality, durability and performance. However, it is difficult to
manufacture, so the company producing a titanium chair needs to have
some specialty knowledge when it comes to welding and putting the
frame together.”

Aluminum vs. Titanium: Is a “Hybrid” the Future of Ultralights?

As materials for today’s ultralightweight
wheelchairs, titanium and
aluminum have a lot of good qualities.
Each also has its limitations…not the least
of which, for titanium, is a hefty price tag
that funding sources aren’t always willing
to pay.

Given that federal and state budgets
for health care are unlikely to robustly
grow any time soon, is a good answer to
“Aluminum vs. Titanium” actually “some
of both”?

“Yes,” says TiLite’s Josh Anderson, “I
think a hybrid strategy is a great idea…
in fact, we are already doing this. There
are component applications where it is
better to use titanium and others where
it is better to use aluminum. And we are
not limited to titanium or aluminum.
Today, carbon fiber, stainless steel and
composites are used in our products as
well. In the future, other materials such as
magnesium and ceramics will be tested in
different components in an ongoing effort
to enhance performance.”

Given the fact that titanium can
be challenging to work with, Pride
Mobility Products’ Mike Zablocky says,
“The hybrid strategy may become the
prevailing approach. Using titanium
tubing for the frame, and then aluminum
for other components, such as the axle
plate and the caster forks, the high-stress
areas, may provide additional strength
necessary in areas where you really
need to take care in the manufacturing
process. A titanium axle that’s embrittled
certainly poses more of a risk, so you’d
probably stay with steel and lose the
benefit of the weight, but you’d have
less risk.”

Sunrise Medical’s Tom Whelan points
out that even chairs that are called “titanium”
often feature other materials as
well: “You use titanium in the frame
members of the chair primarily. But a lot
of the elements of the chair are still going
to be aluminum. The caster forks, the axle
system, components that mount the backrest
to the frame – you’re introducing a
lot of other materials other than just pure
titanium.”

Taking advantage of the best that both
materials have to offer may, in the long
run, be even better than choosing one
metal or the other.

“They both have advantages and disadvantages,”
Whelan notes. “That has to
be weighed through design and through
(clients’) need to reach an outcome.”

And the Winner Is…

Five assumptions, plenty of praise for both metals, and possible advantages
for each. So is there a clear “winner” between titanium and
aluminum?

Says McCarthy, “Having come from nearly two decades on the
provider side, as a former practicing ATP, I’ve had consumers that have
ridden both types of chairs, one constructed of aluminum and the same
consumer riding a chair that’s constructed of titanium – with probably
unnotable changes in ride characteristics.”

He calls the two metals “comparable” in their ultralight results,
adding, “I believe in my heart of hearts that titanium and the use or the
application of titanium in any instance – whether it be manual mobility,
custom mobility or shopping carts – it’s definitely a perception issue.
I think if I were to blindfold an end-user and put them in identically
configured rigid chairs, one constructed of titanium, one constructed of
aluminum, they would not be able to tell the difference.”

In fact, about many consumers’ vehement preferences for titanium,
he says, “I think I would get different opinions if I were to poll
consumers – two consumers, one of which was recently injured and
one that was 15 years post-injury. I think that if I were to put them
in two separate rooms, I would get two totally different responses.
Titanium hasn’t been around that long, number one, and it is a perception
thing. I think the word titanium is an exciting sounding word. I
think for these younger folks that are recently injured, it’s something
that they may ride during their rehab stay.”

Black, in his work with Top End, frequently speaks to wheelchair
users at consumer events.

“Everybody talks about weight, and it just consumes our decisions,”
Black says. “It just consumes them. It’s evident in the bicycle industry,
too, because they talk about one or two lbs. difference. (Titanium) is
thousands of dollars’ difference in cost, but what really true advantage
do you have? The reality is on flat surfaces, there’s no true value.
It’s all in the wheels and the components on that bike. It doesn’t have
anything to do with the material.”

In fact, Black suggests, while weight is undeniably important,
choosing the best ultralight for a particular client is much more complex
than simply choosing one metal over the other or selecting the lightest
chair available.

“You can lose five lbs. and be more efficient,” he says. But he
believes the real significance comes from “how that chair is square, and
how you’re fit into that product. In my opinion, that’s the frontier of the
industry: Where our dealers and our clinicians have a lot of strength is
being able to sell the concept of a proper fit. It’s way more important
than the product itself.”

“If you really want to solve problems,” Whelan says, “you look at
design first and materials second. I know I keep coming back to this,
but I think it’s a very important point so we don’t mislead the industry
into thinking that material is a magic bullet.”

Whelan, like the other experts interviewed for this story, says
aluminum and titanium each has its advantages.

“There is no way you can say that one is clearly better than the
other, especially if you bring cost into the mix,” Whelan says (see
sidebar on Aluminum v. Titanium: The Funding Question).

“Titanium has inherent properties that may be taken advantage
of through design to be better than aluminum, relative to vibration.
Aluminum may actually have advantages, especially if you consider
costs, relative to stiffness.

“A stiffer chair is going to be easier to propel, but it’s going to
likely transmit more vibration. A chair that transmits less vibration is
inherently going to absorb more energy that was meant for propulsion.
It’s ‘What’s your design intent, what are you looking for?’ If I’m
an end-user who lives in an environment where I’m primarily on hard,
smooth surfaces, I may want propulsion efficiency and not worry about
vibration.”

Whelan agrees that ultimately, the question of “Which metal is
better?” might be better phrased: “I think the other aspect of this is
‘Who’s the user?’”

Anderson leans toward titanium for its performance qualities, but
for certain applications, he says the field is more level. “As far as transfers
and portability, in my opinion both of these are more a factor of
design than the actual material of the frame.”

He, too, notes the need for ultralight chairs to fit the needs of individual
clients. “These are custom-made ultralightweight wheelchairs
and should be thought of more as a prosthetic. An amputee can’t just
take someone else’s leg and put it on and expect it to work perfectly.
The same holds true with this class of wheelchairs. The user’s ability to
transfer or the portability of the chair will be dependent on the user’s
abilities, the design or shape of the frame, overall weight and a variety
of other factors. It is really not dependent on material.”

The “battle” between aluminum and titanium seems to be too
complex to say that one metal is always the better choice for all clients
and all applications, and the experts instead urged providers, clinicians
and consumers to view ultralightweight wheelchairs as the comprehensive
seating & mobility systems they are.

“The chair is the soul of the person,” Black says. “That whole thing
has to work as one for it to work correctly.”

This article originally appeared in the March 2010 issue of Mobility Management.